The HER-2/erbB-2 (also called neu) gene encodes a transmembrane glycoprotein of Mr 185,000 (p185) possessing intrinsic tyrosine kinase activity (Akiyama et al., 1986, Science 232: 1644) and displaying extensive homology to the epidermal growth factor (EGF) receptor (Coussens et al., 1985, Science 230: 1132).
Several lines of evidence suggest a link between the amplification of HER-2 and neoplastic transformation. Amplification and overexpression of the HER-2 proto-oncogene occurred in human breast and ovarian cancers and correlated with both poor prognosis and decreased survival in patients (Slamon et al., 1987, Science 235: 177; Slamon et al., 1989, Science 244: 707).
In experimental systems, tumor antigen specific cytotoxic T lymphocytes (CTL) are the most powerful immunological mechanism for the elimination of tumors. (Greenberg, 1991, Adv. Immunol. 49: 281). Therefore, tumor specific antigens (Ag) recognized by CTL are likely to function as tumor rejection Ag, capable of inducing protective immunity in vivo.
CTL recognize class I molecules containing peptidic fragments of intracellular proteins that have been transported into endoplasmic reticulum prior to their transfer to the MHC molecule (Germain, 1995, Ann. NY Acad. Sci. 754:114; Heemels & Ploegh, 1995, Annu. Rev. Biochem. 64:463), while the bulk of class II complexed peptides presented to Th cells are degradation products of exogenous or cell surface proteins that enter the biosynthetic pathway of class II molecules via endocytosis and a subsequent fusion with lysosomes (Cresswell, 1994, Annu. Rev. Immunol. 12: 259). CTL are induced when a protein enters the major histocompatibility complex class I (“MHC I” or “class I”) pathway of antigen processing. To enter this pathway the protein must be present in the cytosol of an antigen presenting cell (APC). There it is degraded into peptides which are then transported into the endoplasmic reticulum, where they associate with HLA class I molecules. These peptides are then displayed together with the class I molecules on the cell surface and can serve as an inducer and target of class I restricted antigen-specific CTL (Rothbard et al., 1987, Nature 326: 881).
The priming of an immune response expands and activates “naive” lymphocytes, i.e., those that have not previously seen a given immunogen such that they become “effector” cells that actively respond. Each naive cell has the potential for seeing one and only one antigenic epitope, a situation analogous to a key fitting into a lock. Only those cells that recognize their cognate epitope become effector cells.
T-cells can be of the “helper” or “cytotoxic” type. Helper T cells secrete growth factors for lymphoid cells that stimulate the activation and function of B and T cells. The cytotoxic T cells recognize and either directly, or indirectly, kill cells that express a particular antigen. Like B cells, each T cell has receptors specific for one and only one antigenic epitope. T cell receptors recognize fragments of proteins that are displayed on the cell surface by major histocompatibility complexes (MHC). The in vivo induction of CTL has typically been accomplished by immunization with live virus or cells (Tanaka, et al., J. Immunol., (1991), 147, 3646-52, Wang, et al., J. Immunol., (1995), 4685-4692). A characteristic of DC, a potent subset of APC, is their ability to trigger in vivo responses of naive CD8+ cytotoxic T-lymphocytes (CTL), after being pulsed with antigen (Ridge et al. 1998 Nature 393:474).
Besides their immature (resting or precursor) form, DC exist in two mature states: activated and superactivated. Activated DC can stimulate CD4+ T helper cells, but not CD8+ cytotoxic T cells (CTL), while superactivated DC posses the ability to stimulate CD8+ CTL.
Although tumor cells may express protein antigens that are recognized as foreign by the subject, and immune surveillance may limit the growth and spread of some types of tumors, the immune system does not always protect the subject from lethal human cancers. Such tumors may overwhelm the immune system due to rapid growth and spread and/or the tumor cells may evade immune destruction. Proposed mechanisms for such evasion include, but are not limited to, (1) down-regulation of Class I MHC antigens on the surface of tumor cells resulting in little or no complexing of processed tumor peptide antigens with Class I MHC as required for recognition by cytotoxic T lymphocytes (CTL), (2) a lack of activation of CTL due to little or no expression of Class II MHC molecules by tumor cells such that they cannot directly activate tumor-specific CD4+ helper T cells (which produce signals likely to be needed for CTL activity), (3) a lack of co-stimulation cell surface markers that provide secondary signals for activation of CD4+ helper T cells, and (4) factors produced by tumor cells that suppress anti-tumor responses, such as fas-ligand (Abbas, A. K. et al., Eds., CELLULAR AND MOLECULAR IMMUNOLOGY, 3rd edition, W.B. Saunders Co., 394-405, 1997).
It is therefore desirable to provide a means for eliciting CTL responses against tumor-specific proteins. CTL can be induced either in vivo with vaccines or can be generated in vitro and then be re-infused into the tumor-bearing organism.